1. Field of the Invention
The invention relates generally to an adjustable axial piston machine having a swash plate design and more particularly to such a machine including a rotating cylindrical drum having a plurality of axial cylindrical bores equispaced from the axis of rotation and equiangularly spaced around the axis of rotation and a rotatable drive shaft to rotate the drum. A reciprocable piston is located in each axial cylindrical bore and has its lower end supported in a guide shoe. A pivotable rocker is supported in a bearing box which is concentric with the axis of the drive shaft. The guide shoes slide along a glide path on the flat sliding surface of the rocker and the rocker has two bearing surfaces in the region of the rocker bearing which are separated by the drive shaft for the cylindrical drum.
2. Description of Prior Art
In known axial piston machines of this type, pressure pockets are located in the region of the upper surface of the rocker bearing to permit a pressure release of the rocker and create small adjusting forces and permit high rotational speeds. These pressure pockets are designed as relatively complicated slot systems wherein only a single pressure pocket is always present in each of the two bearing surfaces separated by the drive shaft for the cylindrical drum. The prior art pressure pockets have different complicated shapes and consist, for example, of closed slots in the form of a figure eight or, in another case, of outwardly closed flats in the curved surface of the rocker. These pressure pockets are alternatively under high pressure or under normal operating fluid pressure on the pressure side through bore holes in the rocker during the operation of the axial piston machine. The pressure depends upon whether these boreholes, in the instantaneous operating state, empty into the pressure pockets of the guide shoes or are blocked as disclosed in United Kingdom patent No. 1,355,002.
It is possible to relieve the pressure on the pressure side of the rocker to a certain extent in known axial piston machines but the release forces always pulsate, and only one pressure pocket subject to alternating pressure is available for the loaded bearing surface. Because the frequency of the fluctuations is speed-dependent, dangerous vibrations of the machine occur in the range of certain speeds. The familiar pressure release arrangements are also relatively complicated and therefore are expensive to manufacture especially in special design variations.